Method for fabricating doped polysilicon lines

ABSTRACT

A method of fabricating polysilicon lines and polysilicon gates, the method of including: forming a dielectric layer on a top surface of a substrate; forming a polysilicon layer on a top surface of the dielectric layer; implanting the polysilicon layer with N-dopant species, the N-dopant species essentially contained within the polysilicon layer; implanting the polysilicon layer with a nitrogen containing species, the nitrogen containing species essentially contained within the polysilicon layer.

RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/711,771 filed on Oct. 4, 2004.

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor fabrication;more specifically, it relates a method of fabricating doped polysiliconlines and complementary metal-oxide-silicon (CMOS) doped polysilicongates.

BACKGROUND OF THE INVENTION

Advanced CMOS devices utilize doped polysilicon lines and gates withmetal silicide layers as a method of improving and matching theperformance of N-channel field effect transistors (NFETs) and P-channelfield effect transistors (PFETs). However, controlling the width andsheet resistance of oppositely doped polysilicon lines and gates hasbecome more important and difficult as the widths of polysilicon linesand gates have decreased. Therefore, there is a need for a method offabricating doped polysilicon lines and gates with improved linewidthcontrol.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method of fabricating asemiconductor structure, forming a dielectric layer on a top surface ofa substrate; forming a polysilicon layer on a top surface of thedielectric layer; implanting the polysilicon layer with N-dopantspecies, the N-dopant species essentially contained within thepolysilicon layer; implanting the polysilicon layer with a nitrogencontaining species, the nitrogen containing species essentiallycontained within the polysilicon layer.

BRIEF DESCRIPTION OF DRAWINGS

The features of the invention are set forth in the appended claims. Theinvention itself, however, will be best understood by reference to thefollowing detailed description of an illustrative embodiment when readin conjunction with the accompanying drawings, wherein:

FIGS. 1A through 1D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a first embodiment of the present invention;

FIGS. 2A through 2D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a second embodiment of the present invention;

FIGS. 3A through 3D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a third embodiment of the present invention;

FIG. 4 is a plot of concentration of implanted species versus distancefrom a top surface of a doped polysilicon layer according to the presentinvention;

FIGS. 5A and 5B are partial cross-sectional views illustrating commonintermediate steps for fabricating doped polysilicon lines and gatesaccording to the present invention;

FIG. 6 is a partial cross-sectional view of a problem solved by thepresent invention; and

FIGS. 7A through 7E are partial cross-sectional views illustratingcommon last steps for fabricating doped polysilicon lines and gatesaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described using fabrication of dopedpolysilicon gates as exemplary of the fabrication process of the presentinvention. A doped polysilicon gate should be considered a dopedpolysilicon line used for a specific purpose.

FIGS. 1A through 1D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a first embodiment of the present invention. In FIG. 1A,formed in a silicon substrate 100 are an N-well 105, a P-well 110 andshallow trench isolation (STI) 115. STI 115 may be formed by etching atrench into substrate 100, depositing a dielectric layer on a surface120 of the substrate of sufficient thickness to fill the trench, andthen performing a chemical-mechanical-polishing step to remove excessdielectric layer. However, formation of STI 115 is optional, and STI 115need not be present. Formed on top surface 120 of substrate 100 is agate dielectric layer 125. Formed on a top surface 130 of gatedielectric layer 125 is a polysilicon layer 135. In one example, gatedielectric layer 125 is thermal silicon oxide having a thickness ofbetween about 0.8 nm to about 4 nm. In one example, polysilicon layer135 is undoped polysilicon having a thickness of between about 40 nm toabout 200 nm.

In FIG. 1B, a photoresist layer 140 is formed on a top surface 145 ofpolysilicon layer 135. Photoresist layer 140 is then removed from overP-well 110 by one of by one of any number of photolithographic methodsknown in the art. Then a phosphorus ion implantation is performed.Photoresist layer 140 is of sufficient thickness to about blockphosphorus ion implantation into polysilicon layer 135 over N-well 105.The ion implantation is performed to place the peak (the maximum) of theimplanted phosphorus distribution concentration (in atm/cm³) proximateto top surface 145 of polysilicon layer 135. Proximate is defined hereinas within about 0 nm to about a value of one fourth of the thickness ofpolysilicon layer 135. (See also FIG. 4, distances D1A and D1B). The ionimplantation is further performed so that the concentration distributionprofile of implanted phosphorus is such as to not significantly affectthe overall P dopant level of P-well 110. The phosphorus ion implantconcentration distribution profile is illustrated in FIG. 4 anddescribed infra. In one example, with polysilicon layer 135 having athickness of about 0.15 nm, phosphorus is implanted at a dose of about5E14 atm/cm² to about 5E16 atm/cm² at an energy of about 30 KeV or less.Arsenic may be substituted for phosphorus and the arsenic. In oneexample, with polysilicon layer 135 having a thickness of about 0.15 nm,arsenic is implanted at a dose of about 5E14 atm/cm² to about 5E16atm/cm² at an energy of about 60 KeV or less. Photoresist layer 140 isthen removed. In other examples, the phosphorus and arsenic doses andenergies should be scaled proportionally to the thickness of polysiliconlayer 135.

In FIG. 1C, a photoresist layer 150 is formed on top surface 145 ofpolysilicon layer 135. Photoresist layer 150 is then removed from overN-well 105 by one of any number of photolithographic methods known inthe art. Then a boron ion implantation is performed. Photoresist layer150 is of sufficient thickness to about block boron ion implantationinto polysilicon layer 135 over P-well 110. The ion implantation isperformed to place the peak of the implanted phosphorus distributionconcentration profile proximate to top surface 145 of polysilicon layer135. The ion implantation is further performed so that the concentrationdistribution profile of implanted boron is such as to not significantlyaffect the overall N dopant level of N-well 105. Photoresist layer 150is then removed.

In FIG. 1D, a nitrogen containing species ion implantation is performed.The ion implantation is performed to place the peak of the implantednitrogen species distribution concentration profile proximate to topsurface 145 of polysilicon layer 135. The ion implantation is furtherperformed so that the concentration of implanted nitrogen penetratinginto either gate dielectric layer 125, N-well 105 and P-well 110 is notsignificant. The nitrogen ion implant concentration distribution profileis illustrated in FIG. 4 and described infra. In one example, withpolysilicon layer 135 having a thickness of about 0.15 nm, nitrogen (asN) is implanted at a dose of about 1E14 atm/cm² to about 4E15 atm/cm² atan energy of about 20 KeV or less. Other suitable nitrogen speciesinclude but is not limited to N, N₂, NO, NF₃, N₂O and NH₃. In otherexamples, the nitrogen dose and energy should be scaled proportionallyto the thickness of polysilicon layer 135. The steps illustrated inFIGS. 5A and 5B are next performed.

For the first, as well as the second and third embodiments of thepresent invention, one intent of the phosphorus (or arsenic), boron andnitrogen containing species ion implantations is to keep a maximumamount as possible of implanted species contained within the polysiliconlayer at the time of ion implantation as well as after various laterheat cycles and to keep a minimum amount as possible of implantedspecies from penetrating through the polysilicon layer into theunderlying layers or into the substrate. Thus, the ion implantations areshallow (low energy) with concentration peaks close to the surface ofthe polysilicon and concentration tails that fall off to very lowconcentrations while still within the polysilicon. Thus the implantedspecies is essentially contained within the polysilicon layer. Less thanabout 2E12 atm/cm² of any of the ion implanted species is intended topenetrate into substrate in the case of a polysilicon line or into thegate dielectric layer or N-well or P-well in the gate of polysilicongates.

FIGS. 2A through 2D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a second embodiment of the present invention. FIG. 2A isidentical to FIG. 1A. In FIG. 2B, a nitrogen containing species ionimplantation is performed. The ion implantation is performed to placethe peak of the implanted nitrogen species distribution concentrationprofile proximate to top surface 145 of polysilicon layer 135. The ionimplantation is further performed so that the concentration of implantednitrogen penetrating into either gate dielectric layer 125, N-well 105and P-well 110 is not significant. The nitrogen ion implantconcentration distribution profile is illustrated in FIG. 4 anddescribed infra. In one example, with polysilicon layer 135 having athickness of about 0.15 nm, nitrogen (as N) is implanted at a dose ofabout 1E14 atm/cm² to about 4E14 atm/cm² at an energy of about 20 KeV orless. Other suitable nitrogen species include but is not limited to N₂,NO, NF₃, N₂O and NH₃. In other examples, the nitrogen dose and energyshould be scaled proportionally to the thickness of polysilicon layer135.

In FIG. 2C, a photoresist layer 155 is formed on top surface 145 ofpolysilicon layer 135. Photoresist layer 155 is then removed from overP-well 110 by one of any number of photolithographic methods known inthe art. Then a phosphorus ion implantation is performed. Photoresistlayer 155 is of sufficient thickness to about block phosphorus ionimplantation into polysilicon layer 135 over N-well 105. The ionimplantation is performed to place the peak of the implanted phosphorusdistribution concentration proximate to top surface 145 of polysiliconlayer 135. The ion implantation is further performed so that theconcentration distribution profile of implanted phosphorus is such as tonot significantly affect the overall P dopant level of P-well 110. Thephosphorus ion implant concentration distribution profile is illustratedin FIG. 4 and described infra. In one example, with polysilicon layer135 having a thickness of about 0.15 nm, phosphorus is implanted at adose of about 5E14 atm/cm² to about 5E16 atm/cm² at an energy of about30 KeV or less. Arsenic may be substituted for phosphorus. In oneexample, with polysilicon layer 135 having a thickness of about 0.15 nm,arsenic is implanted at a dose of about 5E14 atm/cm² to about 5E 16atm/cm² at an energy of about 60 KeV or less. In other examples, thephosphorus and arsenic doses and energies should be scaledproportionally to the thickness of polysilicon layer 135. Photoresistlayer 155 is then removed.

In FIG. 2D, a photoresist layer 160 is formed on top surface 145 ofpolysilicon layer 135. Photoresist layer 160 is then removed from overN-well 105 by one of any number of photolithographic methods known inthe art. Then a boron ion implantation is performed. Photoresist layer160 is of sufficient thickness to about block boron ion implantationinto polysilicon layer 135 over P-well 110. The ion implantation isperformed to place the peak of the implanted phosphorus distributionconcentration profile proximate to top surface 145 of polysilicon layer135. The ion implantation is further performed so that the concentrationdistribution profile of implanted boron is such as to not significantlyaffect the overall N dopant level of N-well 105. Photoresist layer 160is then removed. The steps illustrated in FIGS. 5A and 5B are nextperformed.

FIGS. 3A through 3D are partial cross-sectional views illustratinginitial steps for fabricating doped polysilicon lines and gatesaccording to a third embodiment of the present invention. FIG. 3A isidentical to FIG. 1A. In FIG. 3B, a photoresist layer 165 is formed ontop surface 145 of polysilicon layer 135. Photoresist layer 165 is thenremoved from over P-well 110 by one of any number of photolithographicmethods known in the art. Then a phosphorus ion implantation isperformed. Photoresist layer 165 is of sufficient thickness to aboutblock phosphorus ion implantation into polysilicon layer 135 over N-well105. The ion implantation is performed to place the peak of theimplanted phosphorus distribution concentration proximate to top surface145 of polysilicon layer 135. The ion implantation is further performedso that the concentration distribution profile of implanted phosphorusis such as to not significantly affect the overall P dopant level ofP-well 110. The phosphorus ion implant concentration distributionprofile is illustrated in FIG. 4 and described infra. In one example,with polysilicon layer 135 having a thickness of about 0.15 nm,phosphorus is implanted at a dose of about 5E14 atm/cm² to about 5E16atm/cm² at an energy of about 30 KeV or less. Arsenic may be substitutedfor phosphorus. In one example, with polysilicon layer 135 having athickness of about 0.15 nm, arsenic is implanted at a dose of about 5E14 atm/cm² to about 5E16 atm/cm² at an energy of about 60 KeV or less.In other examples, the phosphorus and arsenic doses and energies shouldbe scaled proportionally to the thickness of polysilicon layer 135.

In FIG. 3C, a nitrogen containing species ion implantation is performed.Photoresist layer 165 is of sufficient thickness to about block nitrogenspecies ion implantation into polysilicon layer 135 over N-well 105. Theion implantation is performed to place the peak of the implantednitrogen species distribution concentration profile proximate to topsurface 145 of polysilicon layer 135. The ion implantation is furtherperformed so that the concentration of implanted nitrogen penetratinginto either gate dielectric layer 125 and P-well 110 is not significant.The nitrogen ion implant concentration distribution profile isillustrated in FIG. 4 and described infra. In one example, nitrogen (asN) is implanted at a dose of about 1E14 atm/cm² to about 4E15 atm/cm² atan energy of about 20 KeV or less. In other examples, the nitrogen doseand energy should be scaled proportionally to the thickness ofpolysilicon layer 135. Other suitable nitrogen species include but isnot limited to N₂, NO, NF₃, N₂O and NH₃. Photoresist layer 165 is thenremoved.

In FIG. 3D, a photoresist layer 170 is formed on top surface 145 ofpolysilicon layer 135. Photoresist layer 170 is then removed from overN-well 105 by one of any number of photolithographic methods known inthe art. Then a boron ion implantation is performed. Photoresist layer170 is of sufficient thickness to about block boron ion implantationinto polysilicon layer 135 over P-well 110. The ion implantation isperformed to place the peak of the implanted phosphorus distributionconcentration profile proximate to top surface 145 of polysilicon layer135. The ion implantation is further performed so that the concentrationdistribution profile of implanted boron is such as to not significantlyaffect the overall N dopant level of N-well 105. Photoresist layer 170is then removed. The steps illustrated in FIGS. 5A and 5B are nextperformed.

The present invention may be practiced by (1) fully matching ionimplantation concentration profiles (concentration vs. ion implanteddistance) of N-dopant (i.e. phosphorus or arsenic) and nitrogen speciesat the same distance into the polysilicon, by (2) matching ionimplantation concentration profiles of N-dopant and nitrogen species,within a predetermined concentration range, at the same distances intothe polysilicon, by (3) matching, within a predetermined concentrationrange, the surface concentrations of N-dopant and nitrogen in thepolysilicon, or by (4) by matching, within a predetermined concentrationrange, peak concentrations of N-dopant and nitrogen at the same distanceinto the polysilicon.

FIG. 4 is a plot of concentration of implanted species versus distancefrom a top surface of a doped polysilicon layer according to the presentinvention. In FIG. 4, curve 175 (N-dopant) and 180 (nitrogen species)are illustrated using option (2), matching ion implantationconcentration profiles of N-dopant and nitrogen species, within apredetermined concentration range, at the same distances into thepolysilicon. That is, an equation defining curve 175 and an equationdefining curve 180 would yield, for the same distance from the topsurface of the polysilicon, a concentration of implanted species withinpredetermined range of concentration of each other. In a full ionimplantation profiles match, option (1) curves 175 and 180 wouldoverlay.

In FIG. 4, the N-dopant (phosphorus or arsenic) ion implantationconcentration distribution profile is indicated by curve 175 and thenitrogen species ion implantation concentration distribution profile isindicated by curve 180. While curve 180 is illustrated above curve 175,curve 175 could be above 180. Also curve 175 and curve 180 could crossat one or more points. The exact relationship between curves 175 and 180is determined by the specific ion implant dose and energy or the Ndopant and the specific ion implant dose and energy or the nitrogen. Thesurface distribution concentration C2A of curve 175 and C2B of curve 180occur respectively at distance 0 into the polysilicon layer. In oneexample, C2A is between about 1E18 atm/cm³ and about 1E21 atm/cm³ andconcentration C2B is about 1E18 atm/cm³ and about 1E22 atm/cm³. Theranges of values for C2A and C2B may overlap.

The peak distribution concentration C3A of curve 175 and C3B of curve180 occur respectively proximate to the surface of the polysilicon atdistance D1A and D1B into the polysilicon layer. In one example, C3A isbetween about 1E18 atm/cm³ and about 1E22 atm/cm³ and concentration C3Bis about 1E18 atm/cm³ and about 1E21 atm/cm³. The ranges of values forC3A and C3B may overlap.

In one example D1A is between about 0 nm and about ⅓ the thickness ofthe polysilicon and depth D1B is about 0 nm to about ⅔ the thickness ofthe polysilicon. The ranges for values for D1A and D1B may overlap.

A concentration C1 is defined in FIG. 4 for curve 175 at a distance D2Aand for curve 180 at a distance D2B into the polysilicon layer. D2A isbetween about 10 nm and the thickness of the polysilicon and D2B isbetween about 50% and about 150% of D2A. Concentration C1 is aconcentration at which an insignificant amount to none of the ionimplanted species exists hence essentially the implanted N dopantspecies and implanted nitrogen containing species are contained with thepolysilicon layer. An insignificant amount of implanted species isdefined as an amount of implanted species, that if present, would notsignificantly effect chemical processes or electrical parameters of thepolysilicon layer (or gate dielectric layer or P-well) in which theimplanted species is present.

Table I summarizes the relationship between curve 175 (N Dopant) andcurve 180 (Nitrogen species). TABLE I Minimum Maximum Value Value NDopant Surface Concentration (C2A) about 1E18 atm/cm³ about 1E22 atm/cm³Nitrogen Species Surface about 1E18 atm/cm³ about 1E21 atm/cm³Concentration(C2B_(—) N Dopant Peak Concentration (C3A) about 1E18atm/cm³ about 1E22 atm/cm³ Nitrogen Species Peak about 1E18 atm/cm³about 1E22 atm/cm³ Concentration(C3B) N Dopant Peak Depth (D1A) about 0nm about equal to ⅓ the polysilicon thickness Nitrogen Species PeakDepth (D1B) about 0 nm about equal to ⅔ the polysilicon thickness NDopant and Nitrogen Species Not Applicable about 1E15 atm/cm³Insignificant Concentration (C1) N Dopant Insignificant Concentration 10nm about equal to the full Depth (D2A) thickness of the polysiliconNitrogen Species Insignificant about 150% of D1A about 150% of D2AConcentration Depth (D2B)

Also in FIG. 4, the gate dielectric layer occurs between a distance D3and D4. Distance D3 is the same as the thickness of the polysiliconlayer discussed supra in reference to FIG. 1A and (D4-D3) is thethickness of the gate dielectric layer discussed supra in reference toFIG. 1A.

FIGS. 5A and 5B are partial cross-sectional views illustrating commonintermediate steps for fabricating doped polysilicon lines and gatesaccording to the present invention. In FIG. 5A, polysilicon layer 135(see FIG. 1D, 2D or 3D} is etched into gate electrodes 185A and 185B.Formation of gate electrodes 185A and 185B may be accomplished by one ofany number of plasma etch processes selective to etch polysilicon overoxide well known in the art.

In FIG. 5B, an oxidation is performed to simultaneously grow a thermaloxide layer 190A over sidewalls 195A and a top surface 200A of gateelectrode 185A and a thermal oxide layer 190B over sidewalls 195B and atop surface 200B of gate electrode 185B. The width of gate electrode185A at top surface 200A and the width of gate electrode 185B at topsurface 200B are both about equal to W1. Gate electrode 185A is doped Ptype and gate electrode 185B is doped N type. Gate electrode 185B (andpossibly gate electrode 185A depending upon which embodiment of thepresent invention is used prior to the thermal oxidation step) has alsobeen nitrogenated by the nitrogen ion species ion implantation describedsupra. This reduces (retards) the thermal oxidation rate of N-dopedpolysilicon. In one example, the thermal oxidation rate of N-dopedpolysilicon is retarded to be about the same as the thermal oxidationrate of P-doped polysilicon. An example of a thermal oxidation is afurnace oxidation performed for in about a 97% O₂ and about 3% HCLgenerating gas a temperature of about 750° C. for 35 minutes which willgrow about 40 angstroms of Si)2 on <100> single-crystal silicon. Thesteps illustrated in FIGS. 7A through 7E are next performed.

FIG. 6 is a partial cross-sectional view of a problem solved by thepresent invention. In FIG. 6, the situation that would otherwise prevailif the nitrogen species ion implantation had not been performed. Afterthermal oxidation, gate electrode 190C has a width W2 at a top surface200C (where W2 is less than W1) because N-doped polysilicon oxidizes ata faster rate than P-doped polysilicon. The situation wherein theN-dopant concentration is higher near a top surface 200C of gateelectrode 185C is illustrated.

Table II illustrates the effect of nitrogen species ion implantation:TABLE II Thermal Oxide Thickness Polysilicon Width at Top NitrogenImplant N-doped P-doped N-doped P-doped Energy and Dose PolysiliconPolysilicon Polysilicon Polysilicon NONE 149 Å  61 Å 13 nm 28 nm 6.3KeV, 5E15 atm/cm² 64 Å 58 Å 23 nm 27 nm 6.3 KeV, 1E16 atm/cm² 52 Å 58 Å23 nm 30 nm

FIGS. 7A through 7E are partial cross-sectional views illustratingcommon last steps for fabricating doped polysilicon lines and gatesaccording to the present invention. FIG. 7A is identical to FIG. 5B. InFIG. 7B, dielectric spacers 205A and 205B are formed over thermal oxidelayers 190A and 190B on sidewalls 195A and 195B of gate electrodes 185Aand 185B respectively. Spacers 205A and 205B may be formed by depositionof a conformal material (for example, silicon nitride) followed by areactive ion etch (RIE) to remove the conformal material from surfacesperpendicular to the direction of the ion flux. Next, well known in theart extension and/or halo and source drain ion implants are performed toP+ source drains 210 in N-well 105 and N+ source drains 215 in P-well115. Additional spacers may be formed between various extension, haloand source/drain ion implants.

In FIG. 7C, gate dielectric layer 125 is removed wherever the gatedielectric layer is not protected by gate electrodes 185A and 185B andby spacers 105A and 205B. (The gate dielectric on the sidewalls of thegate electrodes also protects the underlying gate dielectric layer.)Also, thermal oxide layer 190A and 190B on top surfaces 200A and 200B ofgate electrodes 185A and 185B respectively is removed. Gate dielectriclayer 125 and thermal oxide layer 190A and 190B removal may beaccomplished, for example, using a dilute aqueous HF containingsolution.

In FIG. 7D a metal layer 220 is deposited. Metal layer 220 may benickel, titanium, platinum or cobalt. In FIG. 7E, a portion of metallayer 220 in contact with gate electrodes 185A and 185B and with P+source drains 210 and N+ source/drains 215 is converted to a metalsilicide 225 by annealing and removing unreacted metal layer 220 bymethods well known in the art. Fabrication of a PFET 230 and an NFET 235having similar gate electrode linewidths and resistivity is nowcomplete.

Thus, the present invention provides a method of fabricating dopedpolysilicon lines and gates with improved linewidth control.

The description of the embodiments of the present invention is givenabove for the understanding of the present invention. It will beunderstood that the invention is not limited to the particularembodiments described herein, but is capable of various modifications,rearrangements and substitutions as will now become apparent to thoseskilled in the art without departing from the scope of the invention.Therefore, it is intended that the following claims cover all suchmodifications and changes as fall within the true spirit and scope ofthe invention.

1. A method of fabricating a semiconductor structure, comprising:forming a dielectric layer on a top surface of a substrate; forming apolysilicon layer on a top surface of said dielectric layer; implantingsaid polysilicon layer with N-dopant species, said N-dopant speciesessentially contained within said polysilicon layer; implanting saidpolysilicon layer with a nitrogen containing species, said nitrogencontaining species essentially contained within said polysilicon layer.2. The method of claim 1, wherein a peak concentration of said N-dopantspecies is about equal to a peak concentration of said nitrogencontaining species at about a same distance from a top surface of saidpolysilicon layer.
 3. The method of claim 1, wherein a surfaceconcentration of said N-dopant species is about equal to a surfaceconcentration of said nitrogen containing species at about a samedistance from a top surface of said polysilicon layer.
 4. The method ofclaim 1, wherein said N-dopant species and said nitrogen containingspecies have about a same ion implantation concentration profile.
 5. Themethod of claim 1, wherein a surface concentration of said N-dopantspecies is between about 1E18 atm/cm³ to about 1E22 atm/cm³ and asurface concentration of said nitrogen containing species is betweenabout abut 1E18 atm/cm³ to about 1E21 atm/cm³.
 6. The method of claim 1,wherein: wherein a peak concentration of said N-dopant species isbetween about 1E18 atm/cm³ to about 1E22 atm/cm³ and a peakconcentration of said nitrogen containing species is between about 1E18atm/cm³ to about 1E21 atm/cm³; and said peak concentration of saidN-dopant species occurring between a distance of about 0 nm and about ⅓of a thickness of said polysilicon layer from a top surface of saidpolysilicon layer and said peak concentration of said nitrogencontaining species occurring between about 0 nm to about ⅔ of saidthickness of said polysilicon layer from said top surface of saidpolysilicon layer.
 7. The method of claim 1, wherein: said N-dopantspecies is selected from the group consisting of phosphorus and arsenic;and said nitrogen containing species is selected from the groupconsisting of N, N₂, NO, NF₃, N₂O and NH₃.
 8. The method of claim 1,further including: patterning said polysilicon layer into one or morepolysilicon lines; performing a thermal oxidation of sidewalls and topsurfaces of said one or more polysilicon lines to form a thermal oxidelayer, said thermal oxide layer of about uniform thickness.
 9. Themethod of claim 8, wherein said nitrogen containing species retardsoxidation of said one or more polysilicon lines.
 10. The method of claim1, wherein said implanting said polysilicon layer with N-dopant speciesis performed before said implanting said polysilicon layer with saidnitrogen containing species.
 11. The method of claim 1, wherein saidimplanting said polysilicon layer with N-dopant species is performedafter said implanting said polysilicon layer with said nitrogencontaining species.